Rubber compositions often contain a filler, such as carbon black or silica, to attain desired physical properties. For instance, the rubber compositions used in tires normally contain one or more fillers. Carbon black has traditionally been used as a filler in manufacturing tires. However, there is a growing trend toward utilizing silica or a combination of silica and carbon black in tire rubbers to attain improved physical properties, such as wet traction characteristics.
A silica coupling agent is normally employed in rubber compounds that utilize silica as a filler in order to attain more optimal physical characteristics. Various sulfur containing organosilicon compounds are useful as reactive coupling agents. The use of such organosilicon compounds in silica containing rubbers improves physical properties by coupling the silica filler to the rubber. It should be noted that certain organosilicon compounds are also useful as adhesion primers for glass, metals and other substrates.
U.S. Pat. Nos. 3,842,111, 3,873,489 and 3,978,103 disclose the preparation of various sulfur containing organosilicon compounds. These organosilicon compounds are prepared by reacting (1) 2 moles of a compound of the formula: EQU Z-Alk-X
wherein X is a halogen selected from the group consisting of chlorine, bromine or iodine; wherein Z is ##STR2##
wherein R.sup.1 is an alkyl group containing from 1 to 4 carbon atoms or a phenyl group and wherein R.sup.2 is an alkoxy group containing from 1 to 8 carbon atoms, a cycloalkoxy group containing from 5 to 8 carbon atoms or an alkylmercapto group containing from 1 to 8 carbon atoms, wherein Alk is a divalent aliphatic hydrocarbon, an unsaturated hydrocarbon or a cyclic hydrocarbon containing 1 to 18 carbon atoms; with (2) 1 mole of a compound of the formula EQU M.sub.2 S.sub.n
wherein M is an ammonium group or a metal atom and n is a whole number from 2 to 6. Since the two starting materials are liquid, the reaction can take place in the absence of a solvent; however, the utilization of a volatile inert organic solvent is preferred and accordingly such an inert organic solvent is generally used. The reaction is carried out with the exclusion of water. The reason for the exclusion of water is to avoid the alkaline hydrolysis reaction of the silyl alkoxy groups which will ultimately lead to insoluble polymeric by-products and lower the overall yield of desired product. Aliphatic alcohols, such as methanol, ethanol, iso-propyl alcohol, normal-propyl alcohol, n-butanol, iso-butanol and t-butyl alcohol are representative examples of suitable inert organic solvents. At the end of the reaction between the two starting materials, the separated salt is removed by filtration. The filtrate is then freed from the solvent by distillation under vacuum. Unfortunately, this process is difficult to carry out on a commercial basis for a variety of reasons. For instance, most alcohols that are suitable for utilization as the solvent are difficult to obtain and maintain in a water-free (anhydrous) state. Additionally, most suitable alcohols, such as ethyl alcohol, have a low flash point which is highly undesirable in commercial applications.
U.S. Pat. No. 5,405,985 relates to a process for the production of organosilicon compounds of the formula EQU Z-Alk-S.sub.n -Alk-Z
in which Z is selected from the group consisting of ##STR3##
where
R.sub.1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; PA1 R.sub.2 is alkoxy of 1 to 8 carbon atoms or cycloalkoxy of 5 to 8 carbon atoms; PA1 Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8; comprising reacting (A) a compound of the formula EQU Z-Alk-X PA1 R.sub.1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; PA1 R.sub.2 is alkoxy of 1 to 8 carbon atoms or cycloalkoxy of 5 to 8 carbon atoms; PA1 Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8; comprising reacting (A) a compound of the formula EQU Z-Alk-X PA1 wherein the reaction is conducted in the presence of a phase transfer catalyst, an aqueous phase and a salt of the formula PA1 R.sup.1 is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl; PA1 R.sup.2 is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbon atoms; PA1 Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is an integer of 2 to 8; comprising PA1 (A) reacting sodium hydroxide with sulfur in the presence of a saturated NaCl aqueous solution to form a reaction mixture; and PA1 (B) reacting said reaction mixture with a compound of the formula: EQU Z-Alk-X (II)
where X is Cl, Br or I; with (B) a compound of the formula EQU Me.sub.2 S.sub.n
where Me is an ammonium ion or an alkali metal ion; and wherein the reaction is conducted in the presence of a phase transfer catalyst and an aqueous phase.
U.S. Pat. No. 5,468,893 relates to a process for the production of organosilicon compounds of the formula EQU Z-Alk-S.sub.n -Alk-Z
in which Z is selected from the group consisting of ##STR4##
where
when X is Cl, Br or I; with (B) a compound of the formula EQU Me.sub.2 S.sub.n
where Me is ammonium or an alkali metal;
XY
or EQU X.sub.2 SO.sub.4
where X is selected from the group consisting of Li, Na, K, Rb and Cs; and where Y is selected from the group consisting of F, Cl and Br.
U.S. Pat. No. 5,663,396 discloses a process for the production of organosilicon compounds of the formula EQU Z-Alk-S.sub.n -Alk-Z (I)
in which Z is selected from the group consisting of ##STR5##
where
where X is Cl or Br in the presence of a phase transfer catalyst.